"We have invented elaborate techniques to support this supposedly essential aspect of child development, implementing them at great emotional cost to all parties involved."

In his book, Reiss shares his theory that sleeping separately we’ve created a society of people who fight more, share less and cares more about themselves than others.

While the answer will differ depending on who you talk to, Reiss tackles his reply literally with a trip throughout history to pinpoint the time when parents began encouraging their children to sleep in their own rooms and why.

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So why do we do it?

Well, apparently the system of sleeping separately appeared in the late 19th century.

"As industrial wealth spread through the Western economies, so did a sense that individual privacy — felt most intently at night — was a hallmark of ‘civilization,'" Reiss wrote.

"In 1928, the behavioural psychologist John Watson argued that children should occupy their own rooms as early as possible for fear that too much coddling would stunt a child’s development."

He also cites physician William Whitty Hall saying co-sleeping societies were like "wolves, hogs and vermin" who "huddle together."

Other reasons include children being scarred by their parents having sex in the same room.

That said, Reiss isn’t suggesting everyone immediately begins co-sleeping. He also points out the benefits to everyone having their own room and that it’s up to the individual to decide.

"It’s more practical for adults to pursue nighttime leisure in an area where children aren’t sleeping; it’s easier to set everyone on a proper schedule for work and school when they can all retire to different spaces at different times; and parental intimacy may increase without little ones around. Doctors advise parents not to share soft mattresses with infants — in case they roll over and suffocate the child — especially if the adults have been drinking before bed,” he said.

But, he ponders the idea, "If we raised our children to share space with each other and their parents at night, they might grow up to fight a bit less, share a bit more, and care for others as much as they care for themselves."